This invention generally relates to electric lamps and has particular reference to an improved halogen-cycle type incandescent lamp and to an improved lamp unit that utilizes the halogen-cycle lamp as a light source component.
Halogen-cycle incandescent lamps are well known in the art and utilize a halogen, such as bromine or iodine, within the envelope which returns vaporized tungsten back to the filament and thus prevents the envelope walls from progressively blackening and drastically reducing the light output of the lamp during its useful life. Due to the high bulb-wall temperatures involved and the use of a halogen-containing atmosphere, the envelopes of such lamps were generally made from quartz. However, in order to reduce the material and manufacturing costs, halogen-cycle incandescent lamps have been developed which employ envelopes that are composed of various kinds of hard glasses. Canadian Pat. No. 763,062, issued July 11, 1967 to L. Bouwman et al., for example, discloses a halogen type incandescent lamp that has a borosilicate glass envelope which contains iodine and a small amount of phosphorus which serves as a getter for residual oxygen and other impurities in the lamp. Halogen incandescent lamps that contain bromine and have borosilicate glass envelopes are also disclosed in U.S. Pat. Nos. 3,641,386 (Audesse et al) and 3,648,094 (DeCaro et al). Various kinds of aluminosilicate glass compositions have also been employed in the manufacture of envelopes for halogen-cycle incandescent lamps, as disclosed in U.S. Pat. Nos. 3,496,401 (Dumbaugh, Jr.); 3,798,491 (Malm) and 3,829,729 (Westlund et al). A halogen-cycle incandescent lamp having an envelope that is fabricated from hard glass (aluminosilicate or borosilicate) which is substantially devoid of alkali, carbon monoxide and water is disclosed in U.S. Pat. No. 4,163,171 (Wurster). The use of a special calcium aluminosilicate type glass as the envelope material for a tungsten-bromine lamp is disclosed in U.S. Pat. No. 3,978,362 (Dumbaugh, Jr. et al).
It is also well known in the art to employ such halogen-cycle incandescent lamps in lamp units of the general lighting or reflector type. Canadian Pat. No. 750,519 issued Jan. 10, 1967 to Meijer et al, for example, discloses a compact halogen-cycle lamp that is mounted within a parabolic reflector. A sealed-beam headlamp which contains a non-oxidizing atmosphere and a compact incandescent lamp of the halogen type that has a quartz envelope is disclosed in U.S. Pat. No. 3,553,520 issued Jan. 5, 1971 to Hicks. A lamp unit that is designed for general lighting service and employs a compact halogen-cycle lamp as the light source component is disclosed in U.S. Pat. No. 3,194,625 (Danko).